The present invention relates generally to improvements in fluid driven hydraulic pumps and more particularly to improvements in fluid driven motors used in such hydraulic pumps to drive the hydraulic pumps.
Fluid actuated hydraulic fluid pressure producing units are shown, for example, in U.S. Pat. No. 3,041,975, issued July 3, 1962 to Atherton et al. and in U.S. Pat. No. 3,463,053, issued Aug. 26, 1969 to Leibundgut, both of these patents being assigned to the assignee in common with that of the present invention.
Fluid actuated hydraulic power units of the type referred to in the above patents are generally intended to use a source of air pressure, such as that commonly available in garages or in industrial applications, and which produce air pressure on the order of 100 psi, to supply high pressure hydraulic fluid at pressures on the order of 10,000 psi to operate hydraulic fluid motors or other hydraulic tools. Such hydraulic power units include a reciprocating piston air motor wherein the piston is driven by the compressed air supplied to the air motor and wherein the piston is functional to reciprocate a piston of a hydraulic pump to thereby drive the hydraulic pump and supply high pressure hydraulic fluid through an output passage to a hydraulic tool or the like.
During the operation of such power units, air flows through the air motors at relatively high velocities and as a result, unrestricted air flow through such power units generates a substantial amount of noise. The prior art apparatus has included muffling devices such as muffling materials placed in the exhaust passages of the power units in order to reduce the noise generated by the fluid motors. However, use of muffling materials generates back pressure in the fluid motor thereby decreasing its efficiency of operation and also functioning to reduce the speed of the fluid motor.